1. Field of the Invention
The present invention relates to a bearing race member basically made of structural carbon steel.
2. Prior Art
Unlike other precision machine parts, a ball-and-roller bearing race member or a linear bearing race member (hereinafter referred to as bearing race member) is subjected to extremely high contact stress. Therefore, bearing race members must have superior bearing fatigue strength (so-called bearing life and hereafter simply referred to as "life"). High-carbon chromium bearing steel containing 0.95 to 1.10% C, 1.30 to 1.60% Cr, 0.15 to 0.35% Si, 0.50% or less Mn, 0.025% or less P and 0.025% or less S by weight (equivalent to SUJ2 of JIS) has been mainly used to satisfy the high bearing fatigue strength. Because the above-mentioned high-carbon chromium bearing steel includes abundant alloy elements, segregation of the alloy elements occurs in the solidifying process during steel manufacturing. Eliminating this segregation requires a soaking treatment wherein the steel is heated at a high temperature for a long time (for example at 1,200.degree. C. for 12 hours). In addition, the cost of the steel is high because it includes chromium. For unsevere bearing applications, structural carbon steel (less expensive than the high-carbon chromium bearing steel) containing 0.45 to 0.65% C (equivalent to S45C or S55C of JIS) is sometimes used after the bearing race surface is hardened by induction. However, structural carbon steel is inferior to high-carbon chromium bearing steel in that the life of the former is less than half of that of the latter.